Previous biochemical studies have indicated a role in DNA metabolism for the Escherichia coli DNA-binding protein. An approach to further elucidate the mechanism of action of this and similar proteins and to study its regulation is to determine how their levels fluctuate under various physiological conditions, following DNA-damaging procedures by chemicals or UV light and after bacteriophage infection. The E. coli DNA-binding protein also binds to some DNA polymerases and nucleases in the absence of DNA. These interactions will be further studied with respect to changes in enzymic properties and the association with other cellular proteins investigated. Similar experiments will be performed with the DNA-binding proteins induced by bacteriophage T7 and T3. In bacteriophage T7 only eight phage genes appear to be involved in DNA replication. The role of genes 2,3,3.5, and 6 and DNA-binding protein in the formation and maturation or replicative intermediates will be investigated by an in vitro complementation reaction. DNA, made in cells infected with bacteriophage T7 mutant in one or more of the above genes will be added to DNA-negative extracts of T7-infected cells and the fate of the DNA determined by physical techniques.